Three-Dimensional Printing System Employing A Thermotropic Liquid Crystalline Polymer

ABSTRACT

A three-dimensional printing method is provided. The method comprises selectively forming a three-dimensional structure from a polymer composition. The polymer composition comprises a thermotropic liquid crystalline polymer and exhibits a complex viscosity of from about 50 to about 1,000 Pa-s, as determined by a parallel plate rheometer at an angular frequency of 0.63 radians per second, constant strain amplitude of 1%, and temperature 15° C. above the melting temperature of the polymer composition.

RELATED APPLICATION

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/948,877, filed on Dec. 17, 2019, which is incorporatedherein in its entirety by reference thereto.

BACKGROUND OF THE INVENTION

Additive manufacturing, also called three-dimensional or 3D printing, isgenerally a process in which a three-dimensional structure isselectively formed from a digital model. Various types ofthree-dimensional printing techniques may be employed, such as fuseddeposition modeling, ink jetting, powder bed fusion (e.g., selectivelaser sintering), powder/binder jetting, electron-beam melting,electrophotographic imaging, and so forth. In a fused depositionmodeling system, for instance, a build material may be extruded throughan extrusion tip carried by a print nozzle of the system, and thendeposited as a sequence of layers on a substrate. The extruded materialfuses to previously deposited material, and solidifies upon a drop intemperature. The position of the print nozzle relative to the substratemay be incremented along an axis (perpendicular to the build plane)after each layer is formed, and the process may then be repeated to forma printed part resembling the digital representation. If desired,supporting layers or structures can also be built underneath overhangingportions or in cavities of printed parts under construction, which arenot supported by the build material itself. The support structureadheres to the part material during fabrication, and is removable fromthe completed printed part when the printing process is complete.Regardless of the particular technique, three-dimensional printing hasbeen more commonly employed to form plastic parts. Unfortunately, itsuse has still been somewhat limited in advanced product applicationsthat require a higher level of material performance, such as highthermal stability and heat resistance, enhanced flow, and goodmechanical properties. One reason for this limitation is that thepolymeric materials commonly employed in three-dimensional printingsystems, such as polylactic acid and polyethylene, generally lack highperformance properties. Conversely, attempts at employing highperformance polymers have often failed as such polymers tend to lack therequisite melt strength and stability required for three-dimensionalprinting.

As such, a need exists for a high performance polymer composition thatcan be readily employed in a three-dimensional printing system.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, athree-dimensional printing method is disclosed that comprisesselectively forming a three-dimensional structure from a polymercomposition. The polymer composition comprises a thermotropic liquidcrystalline polymer and exhibits a complex viscosity of from about 50 toabout 1,000 Pa-s, as determined by a parallel plate rheometer at anangular frequency of 0.63 radians per second, constant strain amplitudeof 1%, and temperature 15° C. above the melting temperature of thepolymer composition.

In accordance with another embodiment of the present invention, aprinter cartridge for use in a three-dimensional printing system isdisclosed that comprises a filament that is formed from a polymercomposition, such as described above. In accordance with yet anotherembodiment of the present invention, a three-dimensional printing systemis disclosed that comprises a supply source containing a polymercomposition, such as described above, and a nozzle that is configured toreceive the polymer composition from the supply source and deposit thecomposition onto a substrate. In accordance with still anotherembodiment of the present invention, a three-dimensional printing systemis disclosed that comprises a powder supply comprising a plurality ofparticles formed from a polymer composition, such as described above; apowder bed configured to receive the powder supply; and an energy sourcefor selectively fusing the powder supply when present within the powderbed.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE FIGURES

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a front view of one embodiment of a fused deposition modelingsystem that may be employed in the present invention;

FIG. 2 is a perspective view of one embodiment of a three-dimensionalstructure that may be formed from the polymer composition of the presentinvention;

FIGS. 3A-3C are cross-sectional views of FIG. 2 taken along a line3A-3A, depicting a process for forming a three-dimensional structure;

FIG. 4 is an exploded perspective view of one embodiment of a printercartridge that may be employed in the present invention; and

FIG. 5 is a schematic view of one embodiment of a powder bed fusionsystem that may be employed in the present invention.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention.

Generally speaking, the present invention is directed to athree-dimensional printing system and method that employs a polymercomposition that contains a thermotropic liquid crystalline polymer. Byselectively controlling the specific nature of the liquid crystallinepolymer and other aspects of the composition, the present inventors havediscovered that the resulting composition can achieve certain uniqueproperties that enable the composition to be readily employed in athree-dimensional printing system. More particularly, the compositionmay exhibit a high degree of melt strength, which facilitates itsability to be three-dimensionally printed without losing its physicalintegrity. This high degree of melt strength may be characterized by arelatively high complex viscosity, such as from about about 50 to about1,000 Pa-s, in some embodiments from about 60 to about 800 Pa-s, and insome embodiments, from about 80 to about 600 Pa-s, as determined at anangular frequency of 0.63 radians per second, temperature of 15° C.above the melting temperature of the composition, and constant strainamplitude of 1%. The melt strength of the polymer composition may alsobe characterized by its engineering stress. As explained in more detailbelow, such testing may be performed in accordance with the ARES-EVFduring which an extensional viscosity fixture (“EVF”) is used on arotational rheometer to allow the measurement of the material stressversus percent strain. In this regard, the polymer composition can havea relatively high maximum engineering stress even at relatively highpercent strains. For example, the composition can exhibit its maximumengineering stress at a percent strain of from about 0.3% to about 1.5%,in some embodiments from about 0.4% to about 1.5%, and in someembodiments, from about 0.6% to about 1.2%. The maximum engineeringstress may, for instance, range from about 340 kPa to about 600 kPa, insome embodiments from about 350 kPa to about 500 kPa, and in someembodiments, from about 370 kPa to about 420 kPa. Just as an example, ata percent strain of about 0.6%, the composition can exhibit a relativelyhigh engineering stress of 340 kPa to about 600 kPa, in some embodimentsfrom about 350 kPa to about 500 kPa, and in some embodiments, from about360 kPa to about 400 kPa. The elongational viscosity may also range fromabout 350 kPa-s to about 1500 kPa-s, in some embodiments from about 500kPa-s to about 1000 kPa-s, and in some embodiments, from about 600 kPa-sto about 900 kPa-s.

Despite having a relatively high degree of melt strength, the polymercomposition may nevertheless still possess a low melt viscosity at highshear rates. For example, the polymer composition may exhibit a meltviscosity of about 250 Pa-s or less, in some embodiments about 200 Pa-sor less, in some embodiments from about 0.5 to about 150 Pa-s, and insome embodiments, from about 1 to about 100 Pa-s, as determined inaccordance with ISO Test No. 11443:2005 at a shear rate of 1,000 s⁻¹ andtemperature 15° C. above the melting temperature of the composition.

Conventionally, it was believed that polymer compositions that possessesa high degree of melt strength and good flow properties would not alsopossess sufficiently good thermal and mechanical properties to enabletheir use in three-dimensional printing systems. Contrary toconventional thought, however, the polymer composition may possess bothexcellent thermal and mechanical properties. The melting temperature ofthe composition may, for instance, generally range from about 200° C. toabout 400° C., in some embodiments from about 210° C. to about 400° C.,and in some embodiments, from about 250° C. to about 380° C. The meltingtemperature may be determined as is well known in the art usingdifferential scanning calorimetry (“DSC”), such as determined by ISOTest No. 11357-3:2011. In certain cases, the polymer composition mayhave a relatively low melting temperature to help with processabilityduring three-dimensional printing, such as from about 200° C. to about300° C., and in some embodiments, from about 210° C. to about 290° C. Ofcourse, in other embodiments, the polymer composition may have arelatively high melting temperature, such as from about 300° C. to about400° C., and in some embodiments, from about 310° C. to about 380° C.

Even at the melting temperatures noted above, the ratio of thedeflection temperature under load (“DTUL”), a measure of short term heatresistance, to the melting temperature may still remain relatively high.For example, the ratio may range from about 0.5 to about 1.00, in someembodiments from about 0.6 to about 0.95, and in some embodiments, fromabout 0.65 to about 0.85. The specific DTUL values may, for instance,range from about 200° C. to about 350° C., in some embodiments fromabout 210° C. to about 320° C., and in some embodiments, from about 230°C. to about 290° C.

The polymer composition may also possess good tensile and flexuralmechanical properties. For example, the polymer composition may exhibita tensile strength of from about 20 to about 500 MPa, in someembodiments from about 50 to about 400 MPa, and in some embodiments,from about 70 to about 350 MPa; a tensile break strain of about 0.4% ormore, in some embodiments from about 0.5% to about 10%, and in someembodiments, from about 0.6% to about 3.5%; and/or a tensile modulus offrom about 5,000 MPa to about 20,000 MPa, in some embodiments from about8,000 MPa to about 20,000 MPa, and in some embodiments, from about10,000 MPa to about 20,000 MPa. The tensile properties may be determinedat a temperature of 23° C. in accordance with ISO Test No. 527:2012. Thepolymer composition may also exhibit a flexural strength of from about20 to about 500 MPa, in some embodiments from about 50 to about 400 MPa,and in some embodiments, from about 100 to about 350 MPa; a flexuralelongation of about 0.4% or more, in some embodiments from about 0.5% toabout 10%, and in some embodiments, from about 0.6% to about 3.5%;and/or a flexural modulus of from about 5,000 MPa o about 20,000 MPa, insome embodiments from about 8,000 MPa to about 20,000 MPa, and in someembodiments, from about 10,000 MPa to about 15,000 MPa. The flexuralproperties may be determined at a temperature of 23° C. in accordancewith 178:2010.

Various embodiments of the present invention will now be described inmore detail.

I. Polymer Composition

A. Liquid Crystalline Polymer

As indicated, the polymer composition contains one or more liquidcrystalline polymers, generally in an amount of from about 40 wt. % to100 wt. %, in some embodiments from about 50 wt. % to about 99 wt. %,and in some embodiments, from about 60 wt. % to about 95 wt. % of theentire polymer composition. Liquid crystalline polymers are generallyclassified as “thermotropic” to the extent that they can possess arod-like structure and exhibit a crystalline behavior in their moltenstate (e.g., thermotropic nematic state). The liquid crystallinepolymers employed in the polymer composition typically have a meltingtemperature within the ranges noted above. Such polymers may be formedfrom one or more types of repeating units as is known in the art. Aliquid crystalline polymer may, for example, contain one or morearomatic ester repeating units generally represented by the followingFormula (I):

wherein,

ring B is a substituted or unsubstituted 6-membered aryl group (e.g.,1,4-phenylene or 1,3-phenylene), a substituted or unsubstituted6-membered aryl group fused to a substituted or unsubstituted 5- or6-membered aryl group (e.g., 2,6-naphthalene), or a substituted orunsubstituted 6-membered aryl group linked to a substituted orunsubstituted 5- or 6-membered aryl group (e.g., 4,4-biphenylene); and

Y₁ and Y₂ are independently O, C(O), NH, C(O)HN, or NHC(O).

Typically, at least one of Y₁ and Y₂ are C(O). Examples of such aromaticester repeating units may include, for instance, aromatic dicarboxylicrepeating units (Y₁ and Y₂ in Formula I are C(O)), aromatichydroxycarboxylic repeating units (Y₁ is O and Y₂ is C(O) in Formula I),as well as various combinations thereof.

Aromatic hydroxycarboxylic repeating units, for instance, may beemployed that are derived from aromatic hydroxycarboxylic acids, suchas, 4-hydroxybenzoic acid; 4-hydroxy-4′-biphenylcarboxylic acid;2-hydroxy-6-naphthoic acid; 2-hydroxy-5-naphthoic acid;3-hydroxy-2-naphthoic acid; 2-hydroxy-3-naphthoic acid;4′-hydroxyphenyl-4-benzoic acid; 3′-hydroxyphenyl-4-benzoic acid;4′-hydroxyphenyl-3-benzoic acid, etc., as well as alkyl, alkoxy, aryland halogen substituents thereof, and combination thereof. Particularlysuitable aromatic hydroxycarboxylic acids are 4-hydroxybenzoic acid(“HBA”) and 6-hydroxy-2-naphthoic acid (“HNA”). When employed, repeatingunits derived from hydroxycarboxylic acids (e.g., HBA and/or HNA)typically constitute about 40 mol. % or more, in some embodiments about50 mole % or more, in some embodiments from about 55 mol. % to 100 mol.%, and in some embodiments, from about 60 mol. % to about 95 mol. % ofthe polymer.

Aromatic dicarboxylic repeating units may also be employed that arederived from aromatic dicarboxylic acids, such as terephthalic acid,isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenylether-4,4′-dicarboxylic acid, 1,6-naphthalenedicarboxylic acid,2,7-naphthalenedicarboxylic acid, 4,4′-dicarboxybiphenyl,bis(4-carboxyphenyl)ether, bis(4-carboxyphenyl)butane,bis(4-carboxyphenyl)ethane, bis(3-carboxyphenyl)ether,bis(3-carboxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryl andhalogen substituents thereof, and combinations thereof. Particularlysuitable aromatic dicarboxylic acids may include, for instance,terephthalic acid (“TA”), isophthalic acid (“IA”), and2,6-naphthalenedicarboxylic acid (“NDA”). When employed, repeating unitsderived from aromatic dicarboxylic acids (e.g., IA, TA, and/or NDA)typically constitute from about 1 mol. % to about 40 mol. %, in someembodiments from about 2 mol. % to about 30 mol. %, and in someembodiments, from about 5 mol. % to about 25% of the polymer.

Other repeating units may also be employed in the polymer. In certainembodiments, for instance, repeating units may be employed that arederived from aromatic diols, such as hydroquinone, resorcinol,2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene,1,6-dihydroxynaphthalene, 4,4′-dihydroxybiphenyl (or 4,4′-biphenol),3,3′-dihydroxybiphenyl, 3,4′-dihydroxybiphenyl, 4,4′-dihydroxybiphenylether, bis(4-hydroxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryland halogen substituents thereof, and combinations thereof. Particularlysuitable aromatic diols may include, for instance, hydroquinone (“HQ”)and 4,4′-biphenol (“BP”). When employed, repeating units derived fromaromatic diols (e.g., HQ and/or BP) typically constitute from aboutabout 1 mol. % to about 40 mol. %, in some embodiments from about 2 mol.% to about 30 mol. %, and in some embodiments, from about 5 mol. % toabout 25% of the polymer. Repeating units may also be employed, such asthose derived from aromatic amides (e.g., acetaminophen (“APAP”)) and/oraromatic amines (e.g., 4-aminophenol (“AP”), 3-aminophenol,1,4-phenylenediamine, 1,3-phenylenediamine, etc.). When employed,repeating units derived from aromatic amides (e.g., APAP) and/oraromatic amines (e.g., AP) typically constitute from about 0.1 mol. % toabout 20 mol. %, in some embodiments from about 0.5 mol. % to about 15mol. %, and in some embodiments, from about 1 mol. % to about 10% of thepolymer. It should also be understood that various other monomericrepeating units may be incorporated into the polymer. For instance, incertain embodiments, the polymer may contain one or more repeating unitsderived from non-aromatic monomers, such as aliphatic or cycloaliphatichydroxycarboxylic acids, dicarboxylic acids, diols, amides, amines, etc.Of course, in other embodiments, the polymer may be “wholly aromatic” inthat it lacks repeating units derived from non-aromatic (e.g., aliphaticor cycloaliphatic) monomers.

Although by no means required, the liquid crystalline polymer may be a“high naphthenic” polymer in certain embodiments to the extent that itcontains a relatively high content of repeating units derived fromnaphthenic hydroxycarboxylic acids and naphthenic dicarboxylic acids,such as NDA, HNA, or combinations thereof. That is, the total amount ofrepeating units derived from naphthenic hydroxycarboxylic and/ordicarboxylic acids (e.g., NDA, HNA, or a combination of HNA and NDA) istypically about 40 mol. % or more, in some embodiments about 45 mol. %or more, in some embodiments about 50 mol. % or more, in someembodiments, in some embodiments about 55 mol. % or more, and in someembodiments, from about 60 mol. % to about 95 mol. % of the polymer. Forinstance, the repeating units derived from HNA may constitute from about40 mol. % or more, in some embodiments about 50 mol. % or more, in someembodiments about 55 mol. % or more, and in some embodiments, from about55 mol. % to about 85 mol. % of the polymer. In such embodiments, theliquid crystalline polymer may contain the naphthenic monomers (e.g.,HNA and/or NDA) in the amounts specified above in combination withvarious other monomers, such as aromatic hydroxycarboxylic acid(s)(e.g., HBA) in an amount of from about 5 mol. % to about 50 mol. %, andin some embodiments, from about 10 mol. % to about 40 mol. %; aromaticdicarboxylic acid(s) (e.g., IA and/or TA) in an amount of from about 1mol. % to about 40 mol. %, and in some embodiments, from about 5 mol. %to about 25 mol. %; and/or aromatic diol(s) (e.g., BP and/or HQ) in anamount of from about 1 mol. % to about 40 mol. %, and in someembodiments, from about 5 mol. % to about 25 mol. %.

Regardless of the particular constituents and nature of the polymer, theliquid crystalline polymer may be prepared by initially introducing thearomatic monomer(s) used to form the ester repeating units (e.g.,aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid, etc.)and/or other repeating units (e.g., aromatic diol, aromatic amide,aromatic amine, etc.) into a reactor vessel to initiate apolycondensation reaction. The particular conditions and steps employedin such reactions are well known, and may be described in more detail inU.S. Pat. No. 4,161,470 to Calundann; U.S. Pat. No. 5,616,680 toLinstid, III, et al.; U.S. Pat. No. 6,114,492 to Linstid, III, et al.;U.S. Pat. No. 6,514,611 to Shepherd, et al.; and WO 2004/058851 toWaggoner. The vessel employed for the reaction is not especiallylimited, although it is typically desired to employ one that is commonlyused in reactions of high viscosity fluids. Examples of such a reactionvessel may include a stirring tank-type apparatus that has an agitatorwith a variably-shaped stirring blade, such as an anchor type,multistage type, spiral-ribbon type, screw shaft type, etc., or amodified shape thereof. Further examples of such a reaction vessel mayinclude a mixing apparatus commonly used in resin kneading, such as akneader, a roll mill, a Banbury mixer, etc.

If desired, the reaction may proceed through the acetylation of themonomers as known the art. This may be accomplished by adding anacetylating agent (e.g., acetic anhydride) to the monomers. Acetylationis generally initiated at temperatures of about 90° C. During theinitial stage of the acetylation, reflux may be employed to maintainvapor phase temperature below the point at which acetic acid byproductand anhydride begin to distill. Temperatures during acetylationtypically range from between 90° C. to 150° C., and in some embodiments,from about 110° C. to about 150° C. If reflux is used, the vapor phasetemperature typically exceeds the boiling point of acetic acid, butremains low enough to retain residual acetic anhydride. For example,acetic anhydride vaporizes at temperatures of about 140° C. Thus,providing the reactor with a vapor phase reflux at a temperature of fromabout 110° C. to about 130° C. is particularly desirable. To ensuresubstantially complete reaction, an excess amount of acetic anhydridemay be employed. The amount of excess anhydride will vary depending uponthe particular acetylation conditions employed, including the presenceor absence of reflux. The use of an excess of from about 1 to about 10mole percent of acetic anhydride, based on the total moles of reactanthydroxyl groups present is not uncommon.

Acetylation may occur in in a separate reactor vessel, or it may occurin situ within the polymerization reactor vessel. When separate reactorvessels are employed, one or more of the monomers may be introduced tothe acetylation reactor and subsequently transferred to thepolymerization reactor. Likewise, one or more of the monomers may alsobe directly introduced to the reactor vessel without undergoingpre-acetylation.

In addition to the monomers and optional acetylating agents, othercomponents may also be included within the reaction mixture to helpfacilitate polymerization. For instance, a catalyst may be optionallyemployed, such as metal salt catalysts (e.g., magnesium acetate, tin(I)acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassiumacetate, etc.) and organic compound catalysts (e.g., N-methylimidazole).Such catalysts are typically used in amounts of from about 50 to about500 parts per million based on the total weight of the recurring unitprecursors. When separate reactors are employed, it is typically desiredto apply the catalyst to the acetylation reactor rather than thepolymerization reactor, although this is by no means a requirement.

The reaction mixture is generally heated to an elevated temperaturewithin the polymerization reactor vessel to initiate meltpolycondensation of the reactants. Polycondensation may occur, forinstance, within a temperature range of from about 200° C. to about 400°C., in some embodiments from about 210° C. to about 400° C., and in someembodiments, from about 250° C. to about 380° C. For instance, onesuitable technique for forming the aromatic polyester may includecharging precursor monomers and acetic anhydride into the reactor,heating the mixture to a temperature of from about 90° C. to about 150°C. to acetylize a hydroxyl group of the monomers (e.g., formingacetoxy), and then increasing the temperature to from about 200° C. toabout 400° C. to carry out melt polycondensation. As the finalpolymerization temperatures are approached, volatile byproducts of thereaction (e.g., acetic acid) may also be removed so that the desiredmolecular weight may be readily achieved. The reaction mixture isgenerally subjected to agitation during polymerization to ensure goodheat and mass transfer, and in turn, good material homogeneity. Therotational velocity of the agitator may vary during the course of thereaction, but typically ranges from about 10 to about 100 revolutionsper minute (“rpm”), and in some embodiments, from about 20 to about 80rpm. To build molecular weight in the melt, the polymerization reactionmay also be conducted under vacuum, the application of which facilitatesthe removal of volatiles formed during the final stages ofpolycondensation. The vacuum may be created by the application of asuctional pressure, such as within the range of from about 5 to about 30pounds per square inch (“psi”), and in some embodiments, from about 10to about 20 psi.

Following melt polymerization, the molten polymer may be discharged fromthe reactor, typically through an extrusion orifice fitted with a die ofdesired configuration, cooled, and collected. Commonly, the melt isdischarged through a perforated die to form strands that are taken up ina water bath, pelletized and dried. In some embodiments, the meltpolymerized polymer may also be subjected to a subsequent solid-statepolymerization method to further increase its molecular weight.Solid-state polymerization may be conducted in the presence of a gas(e.g., air, inert gas, etc.). Suitable inert gases may include, forinstance, include nitrogen, helium, argon, neon, krypton, xenon, etc.,as well as combinations thereof. The solid-state polymerization reactorvessel can be of virtually any design that will allow the polymer to bemaintained at the desired solid-state polymerization temperature for thedesired residence time. Examples of such vessels can be those that havea fixed bed, static bed, moving bed, fluidized bed, etc. The temperatureat which solid-state polymerization is performed may vary, but istypically within a range of from about 250° C. to about 350° C. Thepolymerization time will of course vary based on the temperature andtarget molecular weight. In most cases, however, the solid-statepolymerization time will be from about 2 to about 12 hours, and in someembodiments, from about 4 to about 10 hours.

B. Other Optional Components

A wide variety of additional additives can also be included in thepolymer composition, such as fillers (e.g., fibers, particulate fillers,etc.), lubricants, impact modifiers, flow modifiers, pigments,antioxidants, stabilizers, surfactants, waxes, flame retardants,anti-drip additives, and other materials added to enhance properties andprocessability.

For instance, a filler may be employed for improving certain propertiesof the polymer composition. When employed, the filler may be employed inthe polymer composition in an amount of from about 10 to about 95 parts,in some embodiments from about 20 to about 90 parts, and in someembodiments, from about 50 to about 85 parts by weight per 100 parts ofthe aromatic polymer(s) employed in the polymer composition. Forinstance, the filler may constitute from about 10 wt. % to about 70 wt.%, in some embodiments from about 20 wt. % to about 60 wt. %, and insome embodiments, from about 30 wt. % to about 60 wt. % of the polymercomposition. The nature of the filler may vary, such as particles,fibers, etc. Fibrous fillers, for instance, may be employed to helpimprove strength. Examples of such fibrous fillers may include thoseformed from glass, carbon, ceramics (e.g., alumina or silica), aramids(e.g., Kevler® marketed by E.I. DuPont de Nemours, Wilmington, Del.),polyolefins, polyesters, etc., as well as mixtures thereof. Glass fibersare particularly suitable, such as E-glass, A-glass, C-glass, D-glass,AR-glass, R-glass, S1-glass, S2-glass, etc., and mixtures thereof.Particulate fillers may also be employed. Clay minerals may beparticularly suitable for use in the present invention. Examples of suchclay minerals include, for instance, talc (Mg₃Si₄O₁₀(OH)₂), halloysite(Al₂Si₂O₅(OH)₄), kaolinite (Al₂Si₂O₅(OH)₄), illite ((K, H₃O)(Al, Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O)]), montmorillonite (Na, Ca)_(0.33)(Al,Mg)₂Si₄O₁₀(OH)₂.nH₂O), vermiculite ((MgFe, Al)₃(Al, Si)₄O₁₀(OH)₂.4H₂O),palygorskite ((Mg, Al)₂Si₄O₁₀(OH).4(H₂O)), pyrophyllite(Al₂Si₄O₁₀(OH)₂), etc., as well as combinations thereof. In lieu of, orin addition to, clay minerals, still other particulate fillers may alsobe employed. For example, other suitable silicate fillers may also beemployed, such as calcium silicate, aluminum silicate, mica,diatomaceous earth, wollastonite, and so forth.

The liquid crystalline polymer and other optional additives may be meltprocessed or blended together. The components may be supplied separatelyor in combination to an extruder that includes at least one screwrotatably mounted and received within a barrel (e.g., cylindricalbarrel) and may define a feed section and a melting section locateddownstream from the feed section along the length of the screw. Theextruder may be a single screw or twin screw extruder. The speed of thescrew may be selected to achieve the desired residence time, shear rate,melt processing temperature, etc. For example, the screw speed may rangefrom about 50 to about 800 revolutions per minute (“rpm”), in someembodiments from about 70 to about 150 rpm, and in some embodiments,from about 80 to about 120 rpm. The apparent shear rate during meltblending may also range from about 100 seconds⁻¹ to about 10,000seconds⁻¹, in some embodiments from about 500 seconds⁻¹ to about 5000seconds⁻¹, and in some embodiments, from about 800 seconds⁻¹ to about1200 seconds⁻¹. The apparent shear rate is equal to 4Q/πR³, where Q isthe volumetric flow rate (“m³/s”) of the polymer melt and R is theradius (“m”) of the capillary (e.g., extruder die) through which themelted polymer flows.

II. Three-Dimensional Printing

As noted above, the unique properties of the polymer composition areparticularly well-suited for forming structures by three-dimensionalprinting. Various types of three-dimensional printing techniques may beemployed, such as extrusion-based systems (e.g., fused depositionmodeling), powder bed fusion, electrophotography, etc. When employed ina fused deposition modeling system, for instance, the polymercomposition may be employed as the build material that forms thethree-dimensional structure and/or the support material that is removedfrom the three-dimensional structure after it is formed. Referring toFIG. 1, for example, one embodiment of an extrusion-based,three-dimensional printer system 10 is shown that may be employed toselectively form a precursor object containing a three-dimensional buildstructure 30 and a corresponding support structure 32. In the particularembodiment illustrated, the system includes a build chamber 12 andsupply sources 22 and 24. As noted above, the polymer composition of thepresent invention may be used to form the build structure 30 and/orsupport structure 32. In those embodiments in which the polymercomposition is only employed in the build structure or the supportstructure, it should be understood any other conventional material canbe employed for the other structure. For example, in certainembodiments, the polymer composition of the present invention may beused to form the build structure 30. In such embodiments, suitablematerials for the support structure 32 may include conventionalmaterials that are soluble or at least partially soluble in water and/oran aqueous alkaline solution, which is suitable for removing supportstructure 32 in a convenient manner without damaging build structure 24.Examples of such materials may include those described in U.S. Pat. No.6,070,107 to Lombardi et al., U.S. Pat. No. 6,228,923 to Lombardi etal., U.S. Pat. No. 6,790,403 to Priedeman et al., and U.S. Pat. No.7,754,807 to Priedeman et al.

The material for the build structure 30 may be supplied to a nozzle 18from the supply source 22 via a feed line 26 and the support materialfor the support structure 32 may be supplied to the nozzle 18 fromsupply source 24 via a feed line 28. The build chamber 12 likewisecontains a substrate 14 and substrate frame 16. The substrate 14 is aplatform on which the build structure 30 and support structure 32 arebuilt. The substrate is supported by a substrate frame 16, which isconfigured to move the substrate 14 along (or substantially along) avertical z-axis. Likewise, the nozzle 18 is supported by a head frame20, which is configured to move the nozzle 18 in (or substantially in) ahorizontal x-y plane above chamber 12. The nozzle 18 is configured forprinting the build structure 30 and the support structure 32 on thesubstrate 14 in a layer-by-layer manner, based on signals provided fromthe controller 34. In the embodiment shown in FIG. 1, for example, thenozzle 18 is a dual-tip extrusion nozzle configured to deposit build andsupport materials from the supply source 22 and the supply source 24,respectively. Examples of such extrusion nozzles are described in moredetail in U.S. Pat. No. 5,503,785 to Crump, et al.; U.S. Pat. No.6,004,124 to Swanson, et al.; U.S. Pat. No. 7,604,470 to LaBossiere, etal., and U.S. Pat. No. 7,625,200 to Leavitt. The system 10 may alsoinclude other print nozzles for depositing build and/or supportmaterials from one or more tips. During a print operation, the frame 16moves the nozzle 18 in the horizontal x-y plane within the build chamber12, and drive mechanisms are directed to intermittently feed the buildand support materials from supply sources 22 and 24. In alternativeembodiments, the nozzle 18 may function as a screw pump, such asdescribed in U.S. Pat. No. 5,764,521 to Batchelder, et al. and U.S. Pat.No. 7,891,964 to Skubic, et al.

The system 10 may also include a controller 34, which may include one ormore control circuits configured to monitor and operate the componentsof the system 10. For example, one or more of the control functionsperformed by controller 34 can be implemented in hardware, software,firmware, and the like, or a combination thereof. The controller 34 maycommunicate over communication line 36 with chamber 12 (e.g., with aheating unit for chamber 12), the nozzle 18, and various sensors,calibration devices, display devices, and/or user input devices. Thesystem 12 and/or controller 34 may also communicate with a computer 38,which is one or more computer-based systems that communicates with thesystem 12 and/or controller 34, and may be separate from system 12, oralternatively may be an internal component of system 12. The computer 38includes computer-based hardware, such as data storage devices,processors, memory modules, and the like for generating and storing toolpath and related printing instructions. The computer 38 may transmitthese instructions to the system 10 (e.g., to controller 34) to performprinting operations so that the three-dimensional structure areselectively formed.

As shown in FIG. 2, the build structure 30 may be printed onto thesubstrate 14 as a series of successive layers of the build material, andthe support structure 32 may likewise be printed as a series ofsuccessive layers in coordination with the printing of the buildstructure 30. In the illustrated embodiment, the build structure 30 isshown as a simple block-shaped object having a top surface 40, fourlateral surfaces 44 (FIG. 3A), and a bottom surface 46 (FIG. 3A).Although by no means required, the support structure 32 in thisembodiment is deposited to at least partially encapsulate the layers ofbuild structure 30. For example, the support structure 32 may be printedto encapsulate the lateral surfaces and the bottom surface of buildstructure 30. Of course, in alternative embodiments, the system 10 mayprint three-dimensional objects having a variety of differentgeometries. In such embodiments, the system 10 may also printcorresponding support structures, which optionally, at least partiallyencapsulate the three-dimensional objects.

FIGS. 3A-3C illustrate the process of for printing the three-dimensionalbuild structure 24 and support structure 32 in the manner describedabove. As shown in FIG. 3A, each layer of the build structure 30 isprinted in a series of layers 42 to define the geometry of the buildstructure 30. In this embodiment, each layer of the support structure 32is printed in a series of layers 48 in coordination with the printing oflayers 42 of the three-dimensional build structure 30, where the printedlayers 48 of the support structure 32 encapsulate the lateral surfaces44 and the bottom surface 46 of the build structure 30. In theillustrated embodiment, the top surface 40 is not encapsulated by thelayers 48 of the support structure 32. After the print operation iscomplete, the support structure 32 may be removed from the buildstructure 30 to create a three-dimensional object 27. For example, inembodiments in which the support material is at least partially solublein water or an aqueous alkaline solution, the resulting object may beimmersed in water and/or an aqueous alkaline solution bath to dissolvethe support structure 32.

The polymer composition may be supplied to the three-dimensional printerin a variety of different forms, such as in the form of a sheet, film,fiber, filament, pellet, powder, etc. In one particular embodiment, suchas when a fused deposition modeling technique is employed, the polymercomposition may be supplied in the form of a filament as described inU.S. Pat. No. 6,923,634 to Swanson, et al. and U.S. Pat. No. 7,122,246to Comb, et al. The filament may, for example, have an average diameterof from about 0.1 to about 20 millimeters, in some embodiments fromabout 0.5 to about 10 millimeters, and in some embodiments, from about 1to about 5 millimeters. The filament may be included within a printercartridge that is readily adapted for incorporation into the printersystem. The printer cartridge may, for example, contains a spool orother similar device that carries the filament. For example, the spoolmay have a generally cylindrical rim about which the filament is wound.The spool may likewise define a bore or spindle that allows it to bereadily mounted to the printer during use.

Referring to FIG. 4, for example, one embodiment of a spool 186 is shownthat contains an outer rim about which a filament 188 is wound. Agenerally cylindrical bore 190 is also defined within a central regionof the spool 186 about which multiple spokes 225 are axially positioned.Although not required, the printer cartridge may also contain a housingstructure that encloses the spool and thus protects the filaments fromthe exterior environment prior to use. In FIG. 4, for instance, oneembodiment of such a cartridge 184 is shown that contains a canisterbody 216 and a lid 218 that are mated together to define an interiorchamber for enclosing the spool 186. In this embodiment, the lid 218contains a first spindle 227 and the canister body 216 contains a secondspindle (not shown). The spool 186 may be positioned so that thespindles of the canister body and/or lid are positioned within the bore190. Among other things, this can allow the spool 186 to rotate duringuse. A spring plate 222 may also be attached to the inside of the lid218 that has spiked fingers, which are bent to further enhance rotationof the spool 186 in only the direction that will advance filament out ofthe cartridge 184. Although not shown, a guide block may be attached tothe canister body 216 at an outlet 224 to provide an exit path for thefilament 188 to the printer system. The guide block may be fastened tothe canister body 216 by a set of screws (not shown) that can extendthrough holes 232. If desired, the cartridge 184 may be sealed prior touse to help minimize the presence of moisture. For example, amoisture-impermeable material 223 (e.g., tape) may be employed to helpseal the lid 218 to the canister body 216. Moisture can be withdrawnfrom the interior chamber of the canister body 216 through a hole 226,which can thereafter be sealed with a plug 228. A moisture-impermeablematerial 230 may also be positioned over the plug 228 to further sealthe hole 226. Before sealing the cartridge 184, it may be dried toachieve the desired moisture content. For example, the cartridge 184 maybe dried in an oven under vacuum conditions. Likewise, a desiccantmaterial may also be placed within the cartridge 184, such as withincompartments defined by the spokes 225 of the spool 186. Once fullyassembled, the cartridge 184 may optionally be sealed within amoisture-impermeable package.

In addition to being supplied in the form of a filament, the polymercomposition may also be supplied to the fused deposition modeling systemof FIG. 1 in other forms. In one embodiment, for instance, the polymercomposition may be supplied in the form of pellets. For instance, thepellets may be supplied via a hopper (not shown) to a viscosity pump(not shown) that deposits the polymer composition onto the substrate 14.Such techniques are described, for instance, in U.S. Pat. No. 8,955,558to Bosveld, et al., which is incorporated herein by reference. Theviscosity pump may be an auger-based pump or extruder configured toshear and drive successive portions of received pellets and may besupported by a head frame 20 that can move the viscosity pump and/orhopper in the horizontal x-y plane.

Of course, the three-dimensional printing system is by no means limitedto fused deposition modeling. For instance, a powder bed fusion systemmay likewise be employed in certain embodiments of the presentinvention. In such embodiments, the polymer composition is generallyprovided in the form of a powder containing a plurality of particles.The size of the particles may be selectively controlled to helpfacilitate three-dimensional printing. The volume-based median particlesize may, for example, range from about 0.5 to about 200 micrometers, insome embodiments from about 1 to about 100 micrometers, and in someembodiments, from about 2 to about 80 micrometers. The particle sizedistribution may be relatively narrow such that at least 90% by volumeof the microparticles have a size within the ranges noted above.Further, the particles may also be generally spherical to help improveprocessability. Such particles may, for example, have an aspect ratio(ratio of length to diameter) of from about 0.7 to about 1.3, in someembodiments from about 0.8 to about 1.2, and in some embodiments, fromabout 0.9 to about 1.1 (e.g., about 1).

Generally speaking, powder bed fusion involves selectively fusing thepowder within a powder bed to form the three-dimensional structure. Thefusion process may be initiated by an energy source, such as a laserbeam (e.g., laser sintering), electron beam, acoustic energy, thermalenergy, etc. Examples of such systems are described, for instance, inU.S. Pat. Nos. 4,863,538; 5,132,143; 5,204,055; 8,221,858; and9,895,842. Referring to FIG. 5, for example, one embodiment of alasering sintering system is shown. As shown, the system includes apowder bed 301 for forming a three-dimensional structure 303. Moreparticularly, the powder bed 301 has a substrate 305 from which extendssidewalls 302 that together define an opening. During operation, apowder supply 311 is deposited on the substrate 305 in a plurality oflayers to form a build material. A frame 304 is moveable in a verticaldirection (e.g., parallel to the sidewall of the powder bed 301) toposition the substrate 305 in the desired location. A printer head 310is also provided to deposit the powder supply 311 onto the substrate305. The printer head 310 and powder bed 301 may both be provided withina machine frame 301. After the powder supply is deposited, anirradiation device 307 (e.g., laser) emits a light beam 308 onto a workplane 306. This light beam 308 is directed as deflected beam 308′towards the work plane 306 by a deflection device 309, such as arotating mirror. Thus, the powder supply 311 may be depositedlayer-by-layer onto the working surface 305 or a previously fused layer,and thereafter fused at the positions of each powder layer correspondingby the laser beam 8′. After each selective fusion of a layer, the frame304 may be lowered by a distance corresponding to the thickness of thepowder layer to be subsequently applied. If desired, a control system340 may also be employed to control the formation of thethree-dimensional structure on the working surface 305. The controlsystem 305 may include a distributed control system or anycomputer-based workstation that is fully or partially automated. Forexample, the control system 340 may be any device employing ageneral-purpose computer or an application-specific device, which maygenerally include processing devices (e.g., microprocessor), memory(e.g., CAD designs), and/or memory circuitry for storing one or moreinstructions for controlling operation of the printer head 310, powderbed 301, frame 304, and/or deflection device 309.

The following test methods may be employed to determine certain of theproperties described herein.

Test Methods

Melt Viscosity: The melt viscosity (Pa-s) may be determined inaccordance with ISO Test No. 11443:2005 at a shear rate of 1000 s⁻¹ andtemperature 15° C. above the melting temperature (e.g., 350° C.) using aDynisco LCR7001 capillary rheometer. The rheometer orifice (die) had adiameter of 1 mm, length of 20 mm, L/D ratio of 20.1, and an entranceangle of 180°. The diameter of the barrel was 9.55 mm+0.005 mm and thelength of the rod was 233.4 mm.

Complex Viscosity: Complex viscosity is a frequency-dependent viscosity,determined during forced harmonic oscillation of shear stress at angularfrequencies of 0.1 to 500 radians per second. Prior to testing, thesample is cut into the shape of a circle (diameter of 25 mm) using ahole-punch. Measurements are determined at a temperature 15° C. abovethe melting temperature (e.g., 350° C. or 375° C.) and at a constantstrain amplitude of 1% using an ARES-G2 rheometer (TA Instruments) witha parallel plate configuration (25 mm plate diameter). The gap distancefor each sample is adjusted according to the thickness of each sample.

Melt Elongation: Melt elongation properties (i.e., stress, strain, andelongational viscosity) may be determined in accordance with theARES-EVF: Option for Measuring Extensional Velocity of Polymer Melts, A.Franck, which is incorporated herein by reference. In this test, anextensional viscosity fixture (“EVF”) is used on a rotational rheometerto allow the measurement of the engineering stress at a certain percentstrain. More particularly, a thin rectangular polymer melt sample isadhered to two parallel cylinders: one cylinder rotates to wind up thepolymer melt and lead to continuous uniaxial deformation in the sample,and the other cylinder measures the stress from the sample. Anexponential increase in the sample length occurs with a rotatingcylinder. Therefore, the Hencky strain (ε_(H)) is determined as functionof time by the following equation: ε_(H)(t)=ln(L(t)/L_(o)), where L_(o)is the initial gauge length of and L(t) is the gauge length as afunction of time. The Hencky strain is also referred to as percentstrain. Likewise, the elongational viscosity is determined by dividingthe normal stress (kPa) by the elongation rate (s⁻¹). Specimens testedaccording to this procedure have a width of 1.27 mm, length of 30 mm,and thickness of 0.8 mm. The test may be conducted at the meltingtemperature (e.g., about 360° C.) and elongation rate of 2 s⁻¹.

Melting Temperature: The melting temperature (“Tm”) may be determined bydifferential scanning calorimetry (“DSC”) as is known in the art. Themelting temperature is the differential scanning calorimetry (DSC) peakmelt temperature as determined by ISO Test No. 11357-2:2013. Under theDSC procedure, samples were heated and cooled at 20° C. per minute asstated in ISO Standard 10350 using DSC measurements conducted on a TAQ2000 Instrument.

Deflection Temperature Under Load (“DTUL”): The deflection under loadtemperature may be determined in accordance with ISO Test No. 75-2:2013(technically equivalent to ASTM D648-07). More particularly, a teststrip sample having a length of 80 mm, thickness of 10 mm, and width of4 mm may be subjected to an edgewise three-point bending test in whichthe specified load (maximum outer fibers stress) was 1.8 Megapascals.The specimen may be lowered into a silicone oil bath where thetemperature is raised at 2° C. per minute until it deflects 0.25 mm(0.32 mm for ISO Test No. 75-2:2013).

Tensile Modulus, Tensile Stress, and Tensile Elongation: Tensileproperties may be tested according to ISO Test No. 527:2012 (technicallyequivalent to ASTM D638-14). Modulus and strength measurements may bemade on the same test strip sample having a length of 80 mm, thicknessof 10 mm, and width of 4 mm. The testing temperature may be 23° C., andthe testing speeds may be 1 or 5 mm/min.

Flexural Modulus and Flexural Stress: Flexural properties may be testedaccording to ISO Test No. 178:2010 (technically equivalent to ASTMD790-10). This test may be performed on a 64 mm support span. Tests maybe run on the center portions of uncut ISO 3167 multi-purpose bars. Thetesting temperature may be 23° C. and the testing speed may be 2 mm/min.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A three-dimensional printing method comprisingselectively forming a three-dimensional structure from a polymercomposition, wherein the polymer composition comprises a thermotropicliquid crystalline polymer and exhibits a complex viscosity of fromabout 50 to about 1,000 Pa-s, as determined by a parallel platerheometer at an angular frequency of 0.63 radians per second, constantstrain amplitude of 1%, and temperature 15° C. above the meltingtemperature of the polymer composition.
 2. The method of claim 1,wherein the polymer composition exhibits a maximum engineering stress ofabout 200 kPa or more, as determined at the melting temperature of thepolymer composition with an extensional viscosity fixture and arotational rheometer.
 3. The method of claim 1, wherein the polymercomposition exhibits a melt viscosity of about 250 Pa-s or less, asdetermined in accordance with ISO Test No. 11443:2005 at a shear rate of1,000 s⁻¹ and temperature 15° C. above the melting temperature of thepolymer composition.
 4. The method of claim 1, wherein the polymercomposition exhibits a melting temperature of from about 200° C. toabout 400° C.
 5. The method of claim 1, wherein the thermotropic liquidcrystalline polymer contains aromatic ester repeating units, wherein thearomatic ester repeating units include aromatic dicarboxylic acidrepeating units, aromatic hydroxycarboxylic acid repeating units, andaromatic diol repeating units.
 6. The method of claim 5, wherein thearomatic hydroxycarboxylic acid repeating units are derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, or a combinationthereof.
 7. The method of claim 5, wherein the aromatic dicarboxylicacid repeating units are derived from terephthalic acid, isophthalicacid, or a combination thereof.
 8. The method of claim 5, wherein thearomatic diol repeating units are derived from hydroquinone,4,4′-biphenol, or a combination thereof.
 9. The method of claim 1,wherein the thermotropic liquid crystalline polymer has a total amountof repeating units derived from naphthenic hydroxycarboxylic and/ornaphthenic dicarboxylic acids of about 10 mol. % or more.
 10. The methodof claim 1, wherein the polymer composition is selectively extrudedthrough a nozzle to form the three-dimensional structure.
 11. The methodof claim 10, wherein the polymer composition is in the form of afilament.
 12. The method of claim 10, wherein the polymer composition isin the form of a pellet.
 13. The method of claim 1, wherein the polymercomposition is selectively fused to form the three-dimensionalstructure.
 14. The method of claim 13, wherein the polymer compositionis in the form of a powder.
 15. The method of claim 14, wherein thepolymer composition is selectively fused using thermal energy, a laserbeam, electron beam, acoustic energy, or a combination thereof.
 16. Aprinter cartridge for use in a three-dimensional printing system, theprinter cartridge comprising a filament that is formed from a polymercomposition, wherein the polymer composition comprises a thermotropicliquid crystalline polymer and exhibits a complex viscosity of fromabout 50 to about 1,000 Pa-s, as determined by a parallel platerheometer at an angular frequency of 0.63 radians per second, constantstrain amplitude of 1%, and temperature at 15° C. above a meltingtemperature of the polymer composition.
 17. The printer cartridge ofclaim 16, wherein the filament is wound around a rim of a spool.
 18. Athree-dimensional printing system comprising: a supply source containinga polymer composition, wherein the polymer composition comprises athermotropic liquid crystalline polymer and exhibits a complex viscosityof from about 50 to about 1,000 Pa-s, as determined by a parallel platerheometer at an angular frequency of 0.63 radians per second, constantstrain amplitude of 1%, and temperature at 15° C. above a meltingtemperature of the polymer composition; and a nozzle that is configuredto receive the polymer composition from the supply source and depositthe composition onto a substrate.
 19. The system of claim 18, whereinthe supply source is a printer cartridge containing a filament, whereinthe filament comprises the polymer composition.
 20. The system of claim18, wherein the supply source is a hopper containing pellets, whereinthe pellets comprise the polymer composition.
 21. The system of claim20, further comprising a viscosity pump that contains the nozzle,wherein the viscosity pump is configured to receive the pellets from thehopper and extrude the pellets through the nozzle onto the substrate.22. A three-dimensional printing system comprising: a powder supplycomprising a plurality of particles formed from a polymer composition,wherein the polymer composition comprises a thermotropic liquidcrystalline polymer and exhibits a complex viscosity of from about 50 toabout 1,000 Pa-s, as determined by a parallel plate rheometer at anangular frequency of 0.63 radians per second, constant strain amplitudeof 1%, and temperature at 15° C. above a melting temperature of thepolymer composition; a powder bed configured to receive the powdersupply; and an energy source for selectively fusing the powder supplywhen present within the powder bed.
 23. The system of claim 22, whereinthe particles have a volume-based median particle size of from about 0.5to about 200 micrometers.